1. Field of the Invention
The present invention relates to an image forming apparatus for a copying machine, a printer, and so on.
2. Related Background Art
An image forming apparatus using electrophotography has been known, which has a photosensitive drum serving as an image bearing body around which there are provided image forming means such as: a charger means for uniformly charging the photosensitive drum; an exposure means for forming a latent image by illuminating the charged photosensitive drum with light; a developer means for visualizing the latent image with a developer; and a transfer means for transferring the visualized image from the photosensitive drum to a recording medium.
The developer means, for example, sprays the developer from a developer sleeve onto the photosensitive drum. Alternately, the developer may be formed in the shape of a brush on the developer sleeve so as to come into contact with the surface of the photosensitive drum. To obtain good development using either method, the narrow clearance between the surface of the developer sleeve and that of the photosensitive drum must be maintained with high precision.
A developer means has been put to practical use which has rollers at both ends of the developer sleeve, wherein the diameter of the rollers is larger than that of the developer sleeve. The rollers come into contact with respective end portions of the photosensitive drum in order to obtain a predetermined clearance between the surface of the photosensitive drum and that of the developer sleeve.
However, in the arrangement where the spacer rollers are in contact with the photosensitive drum, the mechanical vibration generated when the developer sleeve is driven is transmitted to the photosensitive drum through the rollers. The vibration acts as a load preventing smooth rotation of the photosensitive drum. As a result, the obtained image has defects caused by nonuniformity of the pitch, enlargement or reduction of the image, and so on. Especially in case of a full-color image forming apparatus provided with a plurality of process units, such nonuniformity of the pitch and enlargement or reduction of the image, and so on, result in an image which is irregularly colored and blurred.
As described above, the image forming means arranged close around the image bearing body should act on the image bearing body with high precision, wherein the image bearing body can be easily shaken by the image forming means.